Tire Inflation

[Vaneta]

My trailer tires are the ST ones. TT bought new from the dealer, the inflation pressure they put in all of the tires is 42 PSI with the pressure listed on the tire being 50 psi. On my prior Forest River TT, I had a dealer check everything including tire pressures and get it ready for a trip and later when I checked tire pressure, what they had put in was substantially smaller than that listed on the tire. Making an assumption that what was on the tire was a max pressure, I figured this was okay. However when I brought that up on a forum, everyone was adamant that I needed the higher pressure (50 psi). So I'm getting ready to head 900 miles home....do I leave the tire pressure at 42 psi or raise it?

[Camper_bob]

You should check the yellow sticker on the street side of the trailer. It will list the suggested tire pressure.

That being said, I tow with mine 5 lbs over max sidewall pressure. Or at the very least AT the sidewall max pressure.

References:

http://www.tirerack.com/tires/tirete...jsp?techid=219

"Industry standards dictate tires with the ST designation are speed rated to 65 MPH (104 km/h) under normal inflation and load conditions.

However Goodyear Marathon and Power King Towmax STR tires featuring the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.

Do not exceed the wheel's maximum rated pressure. If the maximum pressure for the wheel prohibits the increase of air pressure, then maximum speed must be restricted to 65 mph (104 km/h).

The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.

Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity."

I don't typically drive more than about 65 at the most, and I'm nowhere close to max loaded conditions for my trailer.

[SouthCo]

Originally Posted by Camper_bob

However Goodyear Marathon and Power King Towmax STR tires featuring the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.

I run my at 50psi and don't typically go above 65 unless passing. I didn't know the above info, so may increase my tires psi... Not to travel any faster but would like that added insurance when passing.

[Vaneta]

I amaze myself at how I can make the simplest thing complicated. As many times as I've referenced that sticker on the side as I've looked at campers and their weights, I forgot about it. I had looked at a sticker on the inside of the camper I'd seen and in the manual which of course has nothing in it for that info. So the sticker on the side says 50 psi. Even though I rarely go over 60 unless passing, that's also good to know on the above. I think I'll be good with 50.
I was befuddled because when I checked the camper tires, they seemed to be underinflated and when I checked car tires, they were 38 psi all around (and should have 35) and that was from the dealer last time I had them rotated. I thought maybe I had a air pressure gremlin traveling with me.

[oldmanAZ]

Originally Posted by Vaneta

...snip....do I leave the tire pressure at 42 psi or raise it?

Raise it to what it says on the sidewall: 50psi.

You should also have the pressure gauge you will be using 'checked.' I've done that by having my service station AND local tire store set different tires at a certain pressure...

"My left tire looked low. Could you please inflate it to (whatever) psi.".

Then check it with your gauge. Not scientific, but it gave me more confidence in my gauge.

[Vaneta]

Well today I was gonna let some air out of my car tires and noticed the gauge had come "unscrewed" a bit so when I tightened it (I finally bought a large non-electronic gauge with a long hose so I could actually see it), car tires were correct at 35 psi. So re-checked trailer and they were still low. I'm guessing from our conversations, the dealer knew I'd be running "light" and figured I might get a better ride or something if it wasn't at max.

[oldmanAZ]

Originally Posted by Vaneta

...snip... I'm guessing from our conversations, the dealer knew I'd be running "light" and figured I might get a better ride or something if it wasn't at max.

IMHO, and off the top of my head, I'd still go with the maximum pressure it says on the tire. Here's why I choose to do that:
1) Lower rolling resistance for better fuel economy.
2) Lower tire temperature from less sidewall flexing (especially when loaded) for longer tire life.
3) Less sidewall flex for better trailer handling (less sway).
4) Less stress on the tire sidewalls when cornering/backing at sharp angles with tandem axles.

[Vaneta]

Well, the third one alone is enough reason for me. I checked out a service station on my way out that has an air hose that's accessible so I think I'll be visiting it in the morning.

[oldmanAZ]

Originally Posted by Vaneta

Well, the third one alone is enough reason for me. I checked out a service station on my way out that has an air hose that's accessible so I think I'll be visiting it in the morning.

If sway is an issue for you when towing, be sure your Tow Vehicle rear tires are inflated to their maximum, too, when you tow. And,if you increase the pressure in your rear tires, you should probably increase the fronts, too, but usually a bit lower than the rears (depending upon the vehicle handling).

Higher tire pressures almost always result in a harsher ride, but that is not dangerous... sway is dangerous.

[bucko]

Originally Posted by oldmanAZ

If sway is an issue for you when towing, be sure your Tow Vehicle rear tires are inflated to their maximum, too, when you tow. And,if you increase the pressure in your rear tires, you should probably increase the fronts, too, but usually a bit lower than the rears (depending upon the vehicle handling).

Higher tire pressures almost always result in a harsher ride, but that is not dangerous... sway is dangerous.

Not sure about this....I was always told to fill the tires of the tow vehicle to the recommended pressure that is listed on the drivers door jamb, and NOT the maximum tire pressure that is listed on the tire sidewall.

Again, this is the vehicle doing the towing, and not the TT.

[Paintinfool3]

I think the tires when towing should be inflated to max sidewall cold pressure . I didnt know about the 10 over on towmaxes but i will be running 60 in mine to try to keep them running cooler as at 50 they seem low looking to me. From what i have read tire pressure on wheels is limited to what the valve stem can handle. . With my tt pushing the limits of the weight on the tires jayco installs i might go to 10 ply maxxis as soon as i can that way i can run 75 psi at least ... i put lt tires on my other tt and what a difference in how it rolled down the road with the 80 psi instead of 50 ... night and day pulling it

[oldmanAZ]

Originally Posted by bucko

Not sure about this....I was always told to fill the tires of the tow vehicle to the recommended pressure that is listed on the drivers door jamb, and NOT the maximum tire pressure that is listed on the tire sidewall.

Again, this is the vehicle doing the towing, and not the TT.

If you don't have any sway when towing, then using lower tire pressures would be fine. On the other hand, if you want to try to reduce sway, try increasing the tire pressure to the tire's maximum. That reduces sidewall flex and that may reduce some or a lot of the sway. It's certainly an easy and cheap thing to try.

There have been folks on this site that have gone to higher load range tires with higher inflation pressures (of course consistent with the tire rim/wheel psi rating). They said that change alone reduced their sway A LOT.

Of course the above is just my opinion and experience. Use the 'search' function on this site and see what others have done to reduce or eliminate sway and see what you think.

[Camper_bob]

When I purchased my trailer, all my tires were at least 10 lbs low, and it was like dragging an elephant. After I referenced the yellow placard, and the sidewall and inflated my TT tires properly (and I check them frequently) it was a whole different towing experience.

As far as inflating the TV tires to max sidewall, here are some notes:
1) For LT tires, they reach their maximum load capacity at max inflation and lower inflation equals lower load carrying capacity. For most 3/4 and 1 ton trucks, you'll see the recommended pressure in the rear is 80 PSI and front is 60 PSI, but most owners only inflate to 80 when they are operating under loaded conditions because lower pressure results in a more comfortable ride when unloaded.
2) For P-rated tires (like those found on most 1/2 ton trucks) their maximum load carrying capacity is reached at lower than max sidewall pressures, and there's a 10% penalty on load capacity for having passenger tires on a truck. So increasing the pressure beyond that recommended will not increase load carrying capacity, but may enhance performance at upper load ranges by not allowing the sidewall to flex as much.

Personally, I tow with my rear tires (P-rated) at max cold inflation per sidewall. However, I don't really notice much difference when towing.

[oldmanAZ]

Originally Posted by Camper_bob

When I purchased my trailer, all my tires were at least 10 lbs low, and it was like dragging an elephant. After I referenced the yellow placard, and the sidewall and inflated my TT tires properly (and I check them frequently) it was a whole different towing experience.

As far as inflating the TV tires to max sidewall, here are some notes:
1) For LT tires, they reach their maximum load capacity at max inflation and lower inflation equals lower load carrying capacity. For most 3/4 and 1 ton trucks, you'll see the recommended pressure in the rear is 80 PSI and front is 60 PSI, but most owners only inflate to 80 when they are operating under loaded conditions because lower pressure results in a more comfortable ride when unloaded.
2) For P-rated tires (like those found on most 1/2 ton trucks) their maximum load carrying capacity is reached at lower than max sidewall pressures, and there's a 10% penalty on load capacity for having passenger tires on a truck. So increasing the pressure beyond that recommended will not increase load carrying capacity, but may enhance performance at upper load ranges by not allowing the sidewall to flex as much.

Personally, I tow with my rear tires (P-rated) at max cold inflation per sidewall. However, I don't really notice much difference when towing.

Thank you, Camper_bob.

I did not know about the P-rated tires and their inflation vs load carrying ability. For those with P-rated tires that is important information.

I have LT tires on my F-350; rears at 80psi, front at 73psi for best load carrying, tire wear, and handling.

[Nighthawk 96]

I have P-rated tires with max psi of 51 lbs per sidewall. Run them at 44 psi towing and fronts at 32 psi, as the WD hitch has returned the front end to its unloaded weight.

Be careful with your TT tire pressure. My wheels are only rate to 60 lbs. I run my tires at 50 lbs cold.

[rbrent]

Where do you find the max rim pressure? I know the tires have it on the side wall but the rims/wheels itself?

[jadatis]

Registed to this forum to react .
Call myself tire-pressure specialist nowadays, story began end 2007 when I got hold of the European Formula sheet from standards manual of ETRTO ( America TRA ) and went running with it.
Gathered a lot of information about tires maximum load and needed pressure.
Now google dayly for it to see if my gathered knowledge can be of use.

Here also the discussion about ST tires .
Made a topic on RV forum for comparing and by that you can get wiser why "maximum pressure" is adviced .

RV.Net Open Roads Forum: How to compare tires for replacement and needed pressure

But to give a start , what most think is maximum pressure is in fact the pressure needed for the maximum load up to maximum speed of tire or if lower 160km/99m/h or for ST 65m/104km/h.
Also called AT-pressure, maxloadpressure, referencef-pressure ( in the formula sheet i got) .
This is not the maximum pressure of a tire , for ST tire makers mostly allow 10 psi extra for higher speed or riding quality.
But you are allowed to drive for instance only 50m/h when filled with adviced pressure for 75m/h. Better for the tires so lesser deflection and lesser heat production.

Wont introduce myself in a seperate topic, dont have an RV anymore, and only react on tire related questions.

Greatings from a Dutch Pigheaded self declared tire-pressure specialist.
( ja dat is ) Peter ( from a dutch name song part of text Yeah thats Peter translated)